A centrifugal separator separates purifies a sample by inserting the sample (for instance, culture solution or blood or the like) into a rotor through a tube or a bucket vessel and rotating the rotor at high speed. A set rotating speed of the rotor is different depending on a use. Products from low speed (about several thousand rotations) to high speed (a maximum rotating speed is 150,000 rpm) are provided so as to meet uses. As rotors to be used, there are various kinds of rotors, for instance, an angle rotor whose tube hole is a fixed angle type so as to meet a high rotating speed or a swing rotor in which a bucket provided with a tube is swung from a vertical state to a horizontal state in accordance with the rotation of the rotor. Further, there are rotors of various sizes such as a rotor that is rotated at a super-high rotating speed to apply a high centrifugal acceleration to a small amount of sample or a rotor that is rotated at a low rotating speed but can treat a large amount of sample. Since these rotors are used depending on the sample to be separated, the rotors are detachably attached to a rotating shaft of a driving unit such as a motor and the rotor may be exchanged.
Generally, an allowable maximum rotating speed of the swing rotor is lower than that of the angle rotor, because the swing rotor has a swing mechanism. The bucket includes a bucket body and a hook portion formed in a cover portion of the bucket body. When the rotation is stopped, the hook portion is engaged with the arm to attach the bucket to the swing rotor. Further, FIGS. 8 and 9 shows related-art, where such structure for holding the bucket by using the hook portion is further improved.
FIG. 8 is an axially longitudinal sectional view of a related-art swing rotor 120. A left half of FIG. 8 shows a rotating state and a right half of FIG. 8 shows a stopping state. In a rotor body 21, four through portions 22 that pass thorough from an upper side to a lower side are provided at equal intervals in the circumferential direction. Buckets 130 are inserted into the through portions 22 from an upper side of the rotor body 21 to a lower side. In upper portions of the buckets 130, pins 134 are extended in directions perpendicular to the longitudinal directions of the buckets 130. Both end portions of the pins 134 abut on lower end portions (not shown in the drawing) of pin insert grooves 23, so that the buckets 130 do not slip out downward from the through portions 22 and are held at positions shown in the right half of FIG. 8. The buckets 130 do not come into contact with the rotor body 21, except for the pins 134. Further, lower end portions of the buckets 130 do not come into contact with a peripheral portion of a driving axial hole 28 of the rotor body 21.
Here, when the swing rotor 120 is rotated, the buckets 130 are swung by a centrifugal force on the pins 134, in the directions shown by an arrow mark 141 as swing shafts (rotating shafts) for a swing movement. In the swing movements of the buckets 130, the buckets 130 are moved from the vertical directions to horizontal directions (immediately transversely). In an outer peripheral side of the rotor body 21, hollow portions 24 are formed which are semi-cylindrically hollowed so as not to block the swing movements of the buckets 130 by the rotor body 21 at that time. The form of the hollow portion 24 may substantially correspond to an outer line of the bucket 130 and may be formed to be slightly larger than the bucket 130 so as to exactly fit the bucket 130 thereto.
The left half of FIG. 8 is a diagram showing a state that the bucket 130 is located in the horizontal direction by the centrifugal force. When the bucket 130 is swung upward until the bucket 130 is located in the horizontal direction, the centrifugal force operates so that the bucket 130 is directed outward in a longitudinal direction of the bucket. A flange portion 132b expanding in a radial direction of the bucket is formed in the bucket. At a higher rotating speed, a contact surface 132a formed in a lower portion of the flange portion 132b comes into contact with a bucket receiving surface 25 formed near an outer peripheral end portion of the hollow portion 24 at a position near an arrow mark 142. In such a way, when the rotating speed of the swing rotor 120 is increased to locate the bucket 130 in the horizontal direction and the centrifugal force of a prescribed level or higher is applied to the bucket 130, the centrifugal load of the bucket 130 is received not by the pin 134, but by the bucket receiving surface 25. Hereinafter, a state that the contact surface 132a of the bucket 130 effectively comes into contact with the bucket receiving surface 25 during a rotation at a sufficiently high rotating speed may be referred to as a “seated state” (The diagram of the left half in FIG. 8 shows a state immediately before the seated state, where the contact surface 132a does not contact the bucket receiving surface 25).
FIG. 9 is a development diagram showing an assembly structure of the related-art bucket 130. The bucket 130 is roughly formed of a cap assembly 131 and a bucket body 132. The bucket body 132 is a vessel for accommodating a tube in which a sample to be separated is put and is formed integrally therewith by scraping metal such as a titanium alloy having high specific strength. In the bucket body 132, a space is formed which corresponds to an outline of the tube and an opening portion 132c is formed for taking in and out the tube in an upper portion. In an inner peripheral side of the opening portion 132c, an internal thread is formed. Further, in a rather lower side of the opening portion 132c of the bucket body 132, the flange portion 132b that expands outwards in the radial direction of the bucket is formed. In the lower side of the flange portion 132b, the contact surface 132a is formed that comes into contact with the rotor body 21. The shape of the contact surface 132a is arbitrary. Here, the contact surface is formed so that the flange portion 132b is smoothly continuous to a lower portion whose diameter is small by a straight line portion and an R portion.
A cap main body 133 as a main portion of the cap assembly 131 serves as a cover for sealing an inner space of the bucket body 132 and is connected to the bucket body 132 by screwing. The cap main body 133 is manufactured, for instance, by scraping a metal alloy such as aluminum and includes a cover portion 133c serving as the cover, a cylindrical portion 133a formed in an upper portion of the cover portion 133c and an external threaded portion 133d formed in a lower portion of the cover portion 133c. The external threaded portion 133d is screwed to the internal threaded portion of the bucket body 132. In the cylindrical portion 133a, a through-hole 133b of an oval form in side view is formed through which the pin 134 transversely penetrates, so as to be vertically movable by a minute distance. The pin 134 is guided by the pin insert groove 23 of the rotor body 21 on both ends thereof and used to hold the bucket 130 on the rotor body 21 so as to swing freely.
A pin holder 135 is a member for attaching the pin 134 to the cap main body 133. When attaching the cap main body 133, the pin 134 and the pin holder 135, the pin holder 135 is initially inserted from an upper end of the cylindrical portion 133a of the cap main body 133. A central position of a through-hole 135a of the pin holder 135 is aligned with a central position of the through-hole 133b of the cap main body 133, and the pin 134 is press fitted in the through-hole 135a of the pin holder 135 from a side, so as to fix the cap main body and the pin holder. Here, the inside diameter of the pin holder 135 is formed with a little clearance so that the pin holder 135 may slide relative to the cylindrical portion 133a of the cap main body 133. Further, since the through-hole 133b formed in the cap main body 133 has the shape of a slot, the pin 134 can move vertically by a minute distance within a range of the through-hole 133b. 
In an upper portion of the pin holder 135, one to several wave washers 136 are inserted and an upper portion thereof is fixed by a stopper 137. The stopper 137 is strongly pressed in and fixed to an upper end of the cylindrical portion 133a of the cap main body 133. The wave washer 136 is a spring member that urges downward the pin 134 and the pin holder 135 which are slightly vertically movable relative to the cap main body 133. When the bucket 130 is supported by both end portions of the pin 134, the pin holder 135 stands still at a position where a repulsion force of the wave washer 136 and a weight of the bucket 130 are balanced.